Wrought austenitic alloy products

ABSTRACT

Wrought alloy products for use in the chemical and food industries, more particularly tubular products such as condenser tubing, super-heater tubing, sheathing for heating elements, and the like. The products are fashioned by extrusion, piercing or other processing from an austenitic chromium-nickel-iron alloy possessing a combination of good hot-workability and good weldability. The wrought products are characterized by a combination of good resistance to intergranular corrosion and excellent resistance to stress-corrosion cracking, even in the presence of chlorides. The alloy, in addition to iron, contains chromium in the amount of 15% to 25%, nickel in amount greater than 25% but less than 35%, manganese 3% to 12%, carbon .06% to .30% with the minimum carbon requirement increasing with descending nickel contents.

United States Patent 1191 Denhard, Jr. et al. 1 Jan. 7, 1975 [5 WROUGHTAUSTENITIC ALLOY 2,894,833 7/1959 Linnert 75/128 PRODUCTS 3,552,9501/1971 Rundeil 75/128 A 3,660,080 5/1972 Espy 75/128 A [75] Inventors:Elbert E. Denhard, Jr., Towson;

5; :2? Gaugh Lumen/me both Primary Examiner-Hyland Bizot Attorney,Agent, or Firm-John Howard Joynt [73] Assignee: Armco Steel Corporation,

Mlddletown, Ohio [57] ABSTRACT [22] filed: 1972 Wrought alloy productsfor use in the chemical and [21] A l N 230,524 food industries, moreparticularly tubular products such as condenser tubing, super-heatertubing, sheath- Related Apphcatwn Data ing for heating elements, and thelike. The products coniinuaiionin-pari of Sen 1 y 1 are fashioned byextrusion, piercing or other process- 19699 abandoneding from anaustenitic chromium-nickel-iron alloy possessing a combination of goodhot-workabi1ity and [521 {LS 75/1289 75/128 F9 75/128 W1 goodweldability. The wrought products are character- 75/128 G ized by acombination of good resistance to intergran- [51] Int. Cl. C22c 31/20ular Corrosion and excellent resistance to Stress- [58] Field of Search75/128 A Corrosion cracking five in the presence of chlorides The alloy,in addition to iron, contains chromium in [56] References Cited theamount of to nickel in amount greater UNITED STATES PATENTS than 25% butless than manganese 3% to 12%, 1,542,233 6/1925 Girin /123 A Carbon 06%to 30% with the minimum Carbon 2,215,734 9/1940 Harder 75/128 Aquircment increasing with descending nickel contents. 2,380,821 7/1945Breeler 75/128 A 2,495,731 1/1950 Jennings 75/128 A 1 Claims, N0Drawings WROUGI'IT AUSTENITIC ALLOY PRODUCTS CROSS-REFERENCE TO RELATEDAPPLICATIONS The present application is a continuation-in-part of ourcopending application Ser. No. 843,738, filed July 22, 1969, andentitled Austenitic Alloy and Product, now abandoned; and may beconsidered as a companion of the Denhard-Espy application Ser. No.491,880, filed Sept. 30, 1965, and entitled Stainless Steel Resistant toStress Corrosion Cracking, now US. Pat. No. 3,495,977 of Feb. 17, 1970,and of the Denhard application Ser. No. 673,242, filed Sept. 18, 1967,and entitled Stress-Corrosion Resistant Stainless Steel," now US. Pat.No. 3,573,034 of Mar. 30, 1971.

As a matter of introduction, our invention is concerned with wroughtproducts, especially tubular products fashioned of the highly alloyedsteels, or more generally, the austenitic chromium-nickel-iron alloys.

Among the objects of our invention is the provision of wrought alloyproducts, such as heat exchangers, condenser tubing, super-heatertubing, and the like. A primary use for this tubing is in electricalgenerating plants powered by nuclear energy wherein a primary, highpurity water system conducts heat from the reactor core and a secondaryheat exchange system conducts tap water for steam generation. We findthat this secondary system requires an alloy capable of withstanding thestress-corrosion propensity of chloridebearing water and yet which lendsitself to ready fabrication into heat exchanger parts. We contemplateseamless tubing and welded tubing as well. These products are also usedin the chemical and food industries, as well as sheathing for heatingelements for furnaces, ovens and stoves; in short, a wide variety ofwrought tubular products for ultimate use at elevated temperatures wherethere may be encountered a combination of oxidation and corrosive attackunder stress.

Other objects of our invention will become apparent from the descriptionwhich follows, or will be particularly pointed to during the course ofthat description.

Accordingly, the invention consists in the combination of elements, thecomposition of ingredients and the relationship of each of the same toone or more of the others, as making up the wrought products andarticles described herein and more especially pointed to in the claimsat the end of this specification.

BACKGROUND OF THE INVENTION As an aid to a better understanding ofcertain features of our invention, it may be well to note at this pointthat there are a number of austenitic chromiumnickel alloys which areavailable to the art and used in the production of wrought tubularproducts. One alloy is INCONEL 600" (about 16% chromium, about 76%nickel, and about 8% iron). Although this alloy enjoys good resistanceto a number of corrosive media, as well as excellent resistance tostress-corrosion cracking, it nevertheless is somewhat lacking instrength. The alloy welds with difficulty, and when used in theas-welded condition is quite susceptible to intercrystalline corrosion.Moreover, the alloy is rather costly because of the high nickelrequirement.

A further chromium-nickel alloy employed in the fabrication of theproducts noted is the Armco 20-4- -5 (about 20% chromium, about 45%nickel, about 5% manganese, about 3% molybdenum, and remainder iron),this forming the subject of the Denhard-Espy US. Pat. No. 3,495,977identified above. While this alloy, like the INCONEL 600, is suited toapplications Where there are encountered substantial stresses in thepresence of a corrosive medium, it, too, is a hsrsqs lizhsqauss 0f th ce requirement Another alloy which is available to the art is IN- COLOY800 (about 21% chromium, about 33% nickel, with remainder iron).Although less costly than INCONEL 600 and Armco 20-45-5, this alloy,like INCONEL 600, welds with difficulty, especially in large sections.Moreover, it is not immune to stress corrosion cracking. It is butmoderately resistant to intercrystalline corrosion.

An austenitic chromium-nickel alloy which is possessed of good weldingproperties forms the subject of the Linnert-Larrimore US. Pat. No.2,894,833, of July 14, 1959, entitled Stainless Steel for Weld. Thatsteel in the form of a weld essentially contains about 12% to 30%chromium, about 7% to 35% nickel, and about 5.5% to 13% manganese. As arod, the steel contains at least 7.1% manganese on up to 16.7% or more,with chromium 12% to 30% and nickel 7% to 35%. (column 4, lines 50-62).Unfortunately, the steel is not characterized by good stress-corrosionproperties, nor, indeed, by superior resistance to intergranular attack.

Of the less expensive austenitic chromium-nickel alloys there recentlyhas been developed a high-carbon stainless steel containing about 23%chromium, about 15% nickel, about .35% carbon, and remainder iron. Thissteel forms the subject of the Denhard US Pat. No. 3,573,034 identifiedabove.

A Heat Resistant Crack Resistant Ductile Steel Weld Deposit is thesubject of Szumachowski US. Pat. No. 3,582,318. Szumachowski dealsspecifically with weld deposits, i.e., metal which has certainproperties in the as-welded condition. He is not concerned with wroughtproducts, especially those employing the composition balance and thenickel-carbon relationship which is critical to the success of theproducts of our invention.

While all of the alloys identified above are possessed of propertieswhich in one respect or another are outstanding, none enjoys acombination of good workability and good weldability, along with goodresistance to corrosive attack under stress and resistance tointercrystalline attack. And although the alloys of low manganesecontent (INCONEL 600 and INCOLOY 800), are employed in the fabricationof wrought tubular products as indicated above, we note that cornerchecks are inclined to develop in fabrication. And elimination of thesechecks is both time consuming and costly. Furthermore, because of theirfully austenitic structure, they are prone to microfissuring when weldedin heavy sections where weld restraint occurs.

SUMMARY OF THE INVENTION One of the objects of our invention, therefore,is to provide wrought chromium-nickel-iron alloy products, particularlywrought tubular products, which overcome the deficiencies inherent incertain products of the prior art and, while readily fabricated by hotand cold methods, also are readily weldable and suited toelevated-temperature applications where there may be encounteredsubstantial stress in the presence of corrosive media.

The wrought products of our invention essentially consist of the fouringredients chromium, nickel, manganese and carbon, with remainderprincipally iron, in which products there is preserved a particularcritical relationship between the four, and especially between thenickel and carbon contents. More particularly, our products essentiallyconsist of about 15% to about 25% chromium, just over 25% to just under35% nickel (that is, 25.5 to 34.5% nickel), about 3% to about 12%manganese, about .06% to about .22% carbon with the carbon requirementincreasing as the nickel content decreases, and remainder substantiallyall iron. Where desired, molybdenum may be present, this in amounts upto about 4% to increase pitting resistance as in chloride media,although this is at the sacrifice of some stresscorrosion resistance.So, too, there may be present one or both of columbium and vanadium intotal amount up to about .7%; for a best combination of results it iscolumbium that is employed, this in the amount of about 0.17% to about0.7%. And for the alloy products of high total alloy content, say about40% or more, we may include the ingredient boron in amounts up to about.0070%, particularly about .0030% or about .0005% to about .0070%. Thenitrogen content is maintained at a mimimum, say not exceeding .03%,because we find that it adversely affects the stress-corrosionproperties. Silicon ordinarily is present in an amount not exceeding1.0%, or for best results, not over .60%. Sulfur and phosphorus areundesirable impurities and usually are kept below .030%.

For a best combination of results we preserve in our alloy products acritical balance between the carbon content on the one hand and thenickel content on the other, as more fully described below. In general,it may be said that best stress-corrosion resisting characteristics arehad with such a carbon-nickel balance. But the higher carbon contentrequired, where there is employed a minimum nickel content, adverselyaffects the intergranular corrosion-resisting properties. So we employno more carbon than is required, especially in the products of thesomewhat higher nickel contents where the higher nickel significantlyrestricts the solubility for carbon.

Now the alloy of interest conveniently is melted in the electric arcfurnace. But where desired, it may be melted in the induction furnaceor, indeed, it may be vacuum melted. Where the cost is justified, thealloy of course may be melted by way of a double melting process, thatis, melted in the electric arc furnace or in the induction furnace, andthe resulting metal in the form of electrodes remelted under vacuumconditions to give a product virtually free of contaminants.

The chromium-nickel-iron alloy in the form of ingots is readilyconverted into slabs, blooms and billets by conventional hot-millpractice, particularly extrusion billets, tube hollows, and the like.And with reheating, the alloy slabs, blooms and billets are furtherconverted into plate, sheet, strip, bars, rod and wire. The extrusionbillets, tube hollows, and the like are fashioned into tubular productsby known extrusion or piercing operations. Still further conversion ofthe plate, sheet, strip, bars, rod and wire, where desired, may be hadby conventional cold-working operations, that is, the metal may becold-rolled into plate, sheet and strip or cold-drawn into wire.

The chromium-nickel-iron alloy of interest lends itself to readyfabrication in the hands of the customerfabricator. The alloy products,when appropriate, may be cut, blanked, bent, drawn, tapped and threaded.The products are characterized by excellent welding properties even incomparatively thick sections, say on the order of several inches. Ofparticular importance, the products are resistant to stress-corrosioncracking, that is, cracking in an environment containing chlorides atelevated temperatures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While in broad composition thewrought alloy products of our invention essentially consist of about 15%to about 25% chromium, just over 25% to just under 35% nickel(particularly 25.5 to 34.5% nickel), about 3% to about 12% manganese,about .06% to .22% carbon with the carbon requirement increasing with adecrease in the nickel content, and remainder principally iron, thereare a number of preferred embodiments in which there is achieved a bestcombination of properties. Actually, for best results, even in ourproducts of broad composition, we find that a particular criticalrelationship must be preserved between the nickel content and the carboncontent. Thus, when the nickel content is just under 35%, that is 34.5%,we find the carbon content must be at least about .06%, for otherwisethe stress-corrosion properties drastically suffer. And so, too, for anickel content of about 30%, the carbon must amount to at least about.07%. With just over 25%, that is 25.5% nickel, the minimum carbonrequirement is about .08%.

With lesser carbon contents than the minimum requirements indicated, wefind that the stress-corrosion properties become wholly inadequate.Although the maximum permissible carbon contents are not as critical asare the minimum values, we find that an excessive carbon contentadversely affects the general corrosion characteristics of the metal,and, moreover, the alloy is inclined to become prohibitively sensitiveto intercrystalline attack. Although we prefer not to be bound byexplanation, we feel that with the higher nickel contents there is anadverse effect upon carbon solubility, with the result that any excessof carbon is not taken into solution, chromium carbides form in thegrain boundaries, this depleting local areas of chromium, andintergranular corrosion-resistance immediately suffers. Best results arehad with a carbon content of about .06% to .l5%, particularly .06% to.l2%, for a nickel content just under 35%; about .0 7% to .l9%, andespecially .07% to .14% carbon, for a nickel content of about 30%; about.08% to .22%, for best results .08% to .l5% carbon, forjust over 25%nickel or 25.5% nickel.

Not only is criticality recognized in the nickel-carbon relationship,but we find it in the nickel content itself. We observe that with thelower nickel contents there is an inclination toward segregation ofcarbides throughout the metal. As a consequence, we conduct thehot-working operations at such temperature as to effect a desireddistribution of carbides; that is, we induce a hot cold-working of themetal, concluding at a temperature not exceeding about 1,700F.,certainly not more than 1,900F. This results in the most favorablestress-corrosion resistance.

With nickel in the amount of 35 or more, hot-workability is adverselyaffected, and so, too, is the weldability of the metal, particularly inlarge section. But in the alloy products according to our invention inwhich nickel is present in maximum amount, that is, about 30% tosomething less than 35%, that is 34.5%, and with carbon present in theamount of about .06% to about .19%, there is enjoyed a best resistanceto stresscorrosion attack, along with substantial resistance tointergranular attack, all without necessity for sharp control ofhot-working temperatures.

While the manganese and chromium contents of our products are by nomeans as critical as the carbonnickel relationship, we nevertheless findthat the manganese content should be at least about 3 or 4%, andpreferably at least about 5% in order to achieve good welding propertiesand good hot-workability. Actually, we find that best weldability is hadwhere manganese is present in the amount of some to 12%. But with thehigh manganese contents the stress-corrosion resistance is inclined tosuffer unless the nickel content is maintained on the high side, thatis, approaching some 35%. And with nickel on the high side, it of coursemakes for a costly product. WM

In our products the chromium content is maintained at a value of atleast about 15%, and preferably at least about 18 or 20%. A chromiumcontent less than about 15% affords insufficient corrosion-resistingcharacteristics. A chromium content exceeding about however, results ina metal which is difficult to work in the hot-mill and, indeed, in thecold-mill as well. For a best combination of results the chromiumcontent is in the amount of about 18% to about 22% or even to about 24%.

One wrought alloy product according to our invention which enjoys acombination of good hot-workability, good weldability and goodresistance to stresscorrosion cracking essentially consists of about 15or 18% to about 24 or 25% chromium, just over 25%, say about 25.5% tojust under 35%, say 34.5% nickel, about 3 or 4% to about 10 or 12%manganese, about- .06% to about .22% carbon with a carbon content ofabout .06% to .15% for a nickel content just under 35% or 34.5%, about.07% to .19% and better yet about .07% to .14% carbon for about nickel,and about .08% to .22% and for best results about .08% to .20% carbonfor just over 25% nickel, with remainder princilt a. f Where desired,for improved strength at high temperatures and improved generalcorrosion-resistance, we may include in the alloy product noted thefurther ingredient molybdenum, this in amounts up to about 4%, andpreferably about 1% to about 3%, but we note that stress-corrosion maysuffer to some extent. So, too, we may include one or both of theingredients columbium and vanadium in total amount up to about .7%,particularly about .1% to about .7% columbium, this to improveintergranular corrosion-resistance and facilitate the processing ofhot-rolled and pickled sheet, strip and plate and pierced, extruded orforged products with an assured freedom from cracking at the corners ofthe same. This is particularly important in the products of even highernickel content. For best results any nitrogen is maintained at a valuenot exceeding .03%. And because of the high total alloy content, boronin an amount up to about .0070%, say about .0005 to about .0070% isemployed.

Another alloy product essentially consists of about 18 or 20% to about24 or 25% chromium, with nickel in the amount of about 25.5% on up toabout 30%, manganese in the amount of about 4% or about 5% on up toabout 10%, with carbon in the amount of about .07% to about .22%,especially about .08% to .22% carbon and particularly .08% to .15% forabout 25.5% nickel and about .07% to .19% carbon and especially .07% to.14% for about 30% nickel. The remainder of the alloy is substantiallyall iron. Here again, however, there may be employed molybdenum inamounts up to about 4%. Also there may be employed columbium and/orvanadium in total amount up to about .7%.

A further alloy product, this enjoying an excellent combination ofresistance to stress-corrosion cracking as well as good resistance tointergranular attack, but at maximum cost because of the nickelrequirement, essentially consists of about 15 or 18% to about 22 or 24%chromium, about 30% to just under 35% nickel, that is about 34 or 34.5%nickel, about 4 or 5% to about 10 or 12% manganese, about .06% to about.19% carbon, the carbon being about .07% to about .19% and especially.O7% to .14% for about 30% nickel and about .06% to about .15%particularly .06% to .12% for just under 35% nickel, and remaindersubstantially all iron. Here again, for a product with best strength andcorrosion-resistance there is included molybdenum in amounts up to about4%, particularly molybdenum in the amount of about 1% to about 3%. Andfor a hotworked and pickled product with best surface and freedom fromcorner cracks, there is included columbium in amounts up to about .7%,more particularly about .1% to about .7%.

An alloy product of best formability in combination with goodhot-workability and resistance to stresscorrosion cracking essentiallyconsists of about 15% to about 25% chromium, about 25.5% to just under35%, that is 34.5% nickel, about 4% to about 10% manganese, about .06%to about .22% carbon with the carbon content amounting to about .06% to.15% especially about .06% to .12% for a nickel content of just under35%, about .07% to .19% especially about .07% to .14% for nickel ofabout 30%, and about .08 to .22% carbon and especially about .08 to .15%for about 25.5% nickel, with columbium and/or vanadium up to about .7%particularly with columbium present in the amount of about .l% to about.7%, and remainder substantially all iron.

As particularly illustrative of the chromium-nickelmanganese-iron alloyof interest, this as compared with the chromium-nickel-manganese alloysof the prior art, there is set out below in Table 1 a series of alloysin terms of chemical composition and resistance to stresscorrosioncracking. In all cases the alloys were in the form of 1/4 inch roundmultinotched samples, annealed at 2,000 F. for 5 minutes, waterquenched,then tested, all in accordance with the procedure set out in theDenhard-Gaugh article appearing in American Society for Testing andMaterials STP-425, September 1967, entitled: Application of anAccelerated Stress-Corrosion Test to Alloy Development. Our samples weresubjected to a loading of 60,000 psi while halfway im mersed in boilingmagnesium chloride solution (42% aqueous solution at a temperature of309 F.) for the times and results indicated.

Table I Chemical Composition and Stress-Corrosion Properties of EightChromiumNickel- Manganese-Iron Wrought Samples Time for FailureHot-Work- Heat No. C Mn Cr Ni Others in Hrs. ability R-3525 .060 .6018.02 34.69 0.16 Cb over 1,000 R-3526 .061 .62 17.94 34.79 0.16 V over1,000 R-354l .061 .61 25.19 36.0 over 1,000 Very poor R-4113 .052 10.4718.32 19.94 6.5 R-4474 .045 9.87 16.16 35.6 65 R-4476 .041 9.84 16.0435.6 2.24 Mo 50 R-7089 .17 .55 22.83 19.81 275 *R-718l .115 4.91 24.0334.00 2.20 Mo over 1,000

Phosphorus less than 03%, sulphur less than .0157, silicon not exceeding.8%.

Careful study of the results presented above in Table 1 rather clearlyreveals that the products of high nickel content and low manganesecontent, with one or more of the further ingredients columbium andvanadium (Heat Nos. R-3525 and R-3526), enjoy great resistance to stressunder severe accelerated corrosive attack, the life being in excess of1,000 hours. These products, unfortunately, however, are characterizedby very poor welding qualities. And, moreover, the hot-workability, asseen from the example in which columbium and vanadium are absent (HeatNo. R-3541), leaves much to be desired. An alloy product with a lesseramount of nickel but also of low manganese content (Heat No. R- 7089),while of acceptable workability, is seen to have a wholly inferior lifeunder stress, namely, 275 hours.

On the other hand, those products containing a large amount of manganesealong with substantial amounts of chromium and nickel (Heat Nos. R-4ll3and R- 4474), while characterized by excellent welding qualities, areseen to have disappointingly low resistance to corrosive attack underconditions of stress, the Heat No. R-4ll3 having a life of only 6.5hours, the Heat No. R-4474 having a life of but 65 hours, and the HeatNo. R-4476 (with 2% molybdenum) having a life of 50 hours. This weattribute to a wholly insufficient carbon content for the amount ofnickel present.

It is only in the alloy product of our invention employing the necessarybalanced relation between the chromium, nickel, manganese and carboncontents, with proper observance of the critical relationship betweenthe nickel and carbon contents, that there is achieved great resistanceto stress under accelerated corrosive attack and yet goodhot-workability and good weldability. This is the alloy Heat No. R-718l,additionally containing molybdenum and columbium,

which enjoys a life exceeding 1,000 hours, along with good weldabilityand good workability.

Thus, in conclusion, it will be seen that we provide in our invention achromium-nickel-manganese-iron wrought alloy product in which there isachieved the various objects hereinbefore set forth. The alloy productemploys a minimum of the expensive ingredient nickel, with controlledquantities of the further ingredients chromium and manganese, all toachieve a metal which works well in the hot-mill, with a minimum of edgecracking or other like defect, which readily lends itself to welding byknown and used techniques, and which is characterized by excellentresistance to cracking under stress in the presence of media containingchlorides at elevated temperatures and by an acceptable level ofresistance to intergranular corrosion.

Inasmuch as many embodiments may be made of our invention, and numerousvariations may be made in the several embodiments herein disclosed, itis to be understood that all matter described herein is to be taken asillustrative and not by way of limitation.

We claim:

1. Wrought austenitic chromium-nickel-iron alloy tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 24% chromium,about 34% nickel, about 5% manganese, about .1% carbon, about 2%molybdenum, about .5% columbium, and remainder substantially all iron. I

2. Wrought austenitic chromium-nickel-iron alloy product characterizedby a combination of good hot-workability, weldability, freedom fromresistance to stress-corrosion cracking and to intergranular attackunder stress at elevated temperatures and essentially consisting ofabout 18% to about 24% chromium, about 30% to nickel, about 4% to about10% manganese, about .15% to about .22% carbon, with the carbon-nickelrelationship being:

Nickel Carbon About 34.5% About .06% to .15% About 30% About .07% to.19% About 25.5% About .08% to .22%

Nickel Carbon About 34.5% About .06% to .15% About 30% About .07% to.19% About 25.5% About .08% to .22%

up to about 3% molybdenum, up to about .7% columbium, with any nitrogennot exceeding .03%, and boron 1 about .22% carbon, with thecarbon-nickel relationship being:

Nickel Carbon About 34.5% About .06% to .15% About 30% About .70% to.19% About 25.5% About 08% to .22%

with any nitrogen not exceeding .03%, up to about 4% molybdenum, up toabout .7% columbium and/or vanadium about 0.0005% to about 0.0070%boron, and remainder substantially all iron.

5. Wrought austenitic chromium-nickel-iron alloy welded tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 18% to about24% chromium, about 30% to about 34.5% nickel, about 3% to about 10%manganese, about .06% to about .19% carbon, about 0.0005% to about0.0070% boron, and remainder substantially all iron.

6. Wrought austenitic chromium-nickel-iron alloy welded tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 15% to about25% chromium, about 25.5% to about 34.5% nickel, about 4% to about 10%manganese, about .06% to about .22% carbon, with the carbonnickelrelationship being:

about .1% to about .7% columbium about 0.0005% to about 0.0070% boron,and remainder substantially all iron.

7. Wrought austenitic chromium-nickel-iron alloy welded tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 18% to about22% chromium, about to about 34.5% nickel, about 4% to about 10%manganese, about .06% to about .19% carbon, about 1% to about 3%molybdenum about 0.0005% to about 0.0070% boron, and remaindersubstantially all iron.

8. Wrought austenitic chromium-nickel-iron alloy welded tubular productsuch as heat exchangers, condenser tubing, super-heater tubing andsheathing for heating elements characterized by a combination ofworkability and resistance to stress-corrosion cracking and tointergranular attack under stress at elevated temperatures andessentially consisting of about 15% to about 25% chromium, about 25.5%to about 34.5%

Nickel Carbon About .06% to .15% About .07% to .19% About 08% to .22%

About 34.5% About 30% About 25.5%

up to about 3% molybdenum, up to about .7% columbium and/or vanadiumabout 0.0005% to about 0.0070% boron, and remainder substantially alliron.

9. Wrought austenitic chromium-nickel-iron alloy sheathing for heatingelements characterized by a combination of workability and resistance tostresscorrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 18% to about24% chromium, about 30% to about 34.5% nickel, about 3% to about 10%manganese, about .06% to about .19% carbon about 0.0005% to about0.0070% boron, and remainder substantially all iron.

1. WROUGHT AUSTENITIC CHROMIUM-NICKEL-IRON ALLOY TUBULAR PRODUCTCHARACTERIZED BY A COMBINATION OF WORKABILITY, RESISTANCE TOSTRESS-CORROSION CRACKING AND TO INTERGRANULAR ATTACK UNDER STRESS ATELEVATED TEMPERATURES AND ESSENTIALLY CONSISTING OF ABOUT 24% CHROMIUM,ABOUT 34% NICKEL, ABOUT 5% MANGANESE, ABOUT .1% CARBON, ABOUT 2%MOLYBDENUM, ABOUT .5% COLUMBIUM, AND REMAINDER SUBSTANTIALLY ALL IRON.2. Wrought austenitic chromium-nickel-iron alloy product characterizedby a combination of good hot-workability, weldability, freedom fromresistance to stress-corrosion cracking and to intergranular attackunder stress at elevated temperatures and essentially consisting ofabout 18% to about 24% chromium, about 30% to nickel, about 4% to about10% manganese, about .15% to about .22% carbon, with the carbon-nickelrelationship being:
 3. Wrought austenitic chromium-nickel-iron alloyproduct characterized by a combination of good hot-workability,weldability, freedom from resistance to stress-corrosion cracking and tointergranular attack under stress at elevated temperatures andessentially consisting of about 18% to about 24% chromium, about 25.5%to about 34.5% nickel, about 3% to about 10% manganese, about .06% toabout .22% carbon, with the carbon-nickel relationship being: 4.Austenitic chromium-nickel-iron alloy welded tubes of the characteremployed in elevated temperature application at high pressurescharacterized by a combination of resistance to stress-corrosioncracking and to intergranular attack under stress at such temperatures,essentially consisting of about 15% to about 25% chromium, about 25.5%to about 34.5% nickel, about 4% to about 12% manganese, about .06% toabout .22% carbon, with the carbon-nickel relationship being:
 5. Wroughtaustenitic chromium-nickel-iron alloy welded tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 18% to about24% chromium, about 30% to about 34.5% nickel, about 3% to about 10%manganese, about .06% to about .19% carbon, about 0.0005% to about0.0070% boron, and remainder substantially all iron.
 6. Wroughtaustenitic chromium-nickel-iron alloy welded tubular productcharacterized by a combination of workability, resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 15% to about25% chromium, about 25.5% to about 34.5% nickel, about 4% to about 10%manganese, about .06% to about .22% carbon, with the carbon-nickelrelationship being:
 7. WroUght austenitic chromium-nickel-iron alloywelded tubular product characterized by a combination of workability,resistance to stress-corrosion cracking and to intergranular attackunder stress at elevated temperatures and essentially consisting ofabout 18% to about 22% chromium, about 30% to about 34.5% nickel, about4% to about 10% manganese, about .06% to about .19% carbon, about 1% toabout 3% molybdenum about 0.0005% to about 0.0070% boron, and remaindersubstantially all iron.
 8. Wrought austenitic chromium-nickel-iron alloywelded tubular product such as heat exchangers, condenser tubing,super-heater tubing and sheathing for heating elements characterized bya combination of workability and resistance to stress-corrosion crackingand to intergranular attack under stress at elevated temperatures andessentially consisting of about 15% to about 25% chromium, about 25.5%to about 34.5% nickel, about 3% to about 12% manganese, about .06% toabout .22% carbon, with the carbon-nickel relationship being:
 9. Wroughtaustenitic chromium-nickel-iron alloy sheathing for heating elementscharacterized by a combination of workability and resistance tostress-corrosion cracking and to intergranular attack under stress atelevated temperatures and essentially consisting of about 18% to about24% chromium, about 30% to about 34.5% nickel, about 3% to about 10%manganese, about .06% to about .19% carbon about 0.0005% to about0.0070% boron, and remainder substantially all iron.